System for detecting a video signal image intensity gradient

DETAILED DESCRIPTION In accordance with the principles of the present invention, it is herein recognized that it is desirable to provide a system for detecting an image intensity gradient such as a luminance gradient that is typically associate with image fading, for example.
The disclosed system may be advantageously used in a video signal processing system including motion compensation to assign a value of zero to motion vectors under certain conditions.
One of these conditions has been described above in the context of an image intensity gradient such as is commonly associated with image fading, where it has been found that zeroing false "motion vectors" significantly reduces or eliminates the described "blockiness" artifacts, and promotes coding efficiency.
In an illustrated embodiment, a sequence of three adjacent image frames is evaluated.
Each frame is partitioned into a similar arrangement of segments.
The sum of the absolute values of differences between similarly located pixels in corresponding segments from adjacent frames is obtained for each of two pairs of adjacent frame segments.
The ratio of the sums of the absolute pixel differences is obtained.
Fading is indicated if the ratio remains substantially constant for a prescribed number of segments.